The present invention generally relates to a source electrode driving circuit for a matrix type liquid crystal display apparatus.
Generally, a matrix type liquid crystal display apparatus, with a switching transistor being added to each of picture elements of the display, is used as a display apparatus for a pocket appliance or the like. This is because the display of high contrast may be provided by the switching function of the transistor even when the multiplex driving operation of multiline has been effected.
The matrix type liquid crystal display apparatus has a switching transistor 51-d built in the display picture-element 51-c of the respective intersecting points between the gate electrode 51-a and the source electrode 51-b provided on one base plate of the liquid crystal panel 51 as shown in FIG. 5. There are provided a gate electrode driving circuit 52 for adding to the respective gate electrodes 51-a scanning pulses. The circuit 52 is adapted to sequentially turn, on the switching transistors of the respective lines. There is further provided a source electrode driving circuit 53 for adding to the respective source electrodes 51-b the voltages corresponding to the varying brightness of the display of the respective picture elements. Further, a controlling circuit 54 is included for controlling the operations of the gate electrode driving circuit 52, the source electrode driving circuit 53 and so on.
The conventional source electrode driving circuit like this is shown in FIG. 6. The source electrode driving circuit is composed of a sampling hold circuit 62 which is adapted to sample and hold the voltages corresponding to the variable brightness of the respective picture elements from the display signal V. It further includes an output buffer circuit 63 which is adapted to simultaneously output into the respective source electrodes 51-b at a timing time T the, voltages Q.sub.1, . . . , Q.sub.n held by the sampling hold circuit 62. Still further, a shift register 61 is included which is adapted to sequentially shift, in accordance with the clock .phi., the sampling signals D for sequentially operating the sampling hold circuit 62 so as to input the outputs q.sub.1, . . . , q.sub.n into the sampling hold circuit corresponding to each column.
As shown in FIG. 7, the display signals V are normally inputted in series for every one picture element. The shift register 61 sequentially shifts the sampling signals D by the clock .phi. to input the outputs q.sub.1, . . . , q.sub.n into the sampling hold circuit corresponding to each column to sequentially cause it to effect the sampling hold operation, Thus, the voltages Vi1, . . . , Vij, . . . , Vin at the moments corresponding to the driving source electrodes among the display signals are held in the sampling hold circuit 62. The held voltages Q.sub.1, . . . , Q.sub.n are simultaneously outputted into each source electrode through the output buffer circuit 63 as shown in FIG. 6.
In this manner, the voltages corresponding to the varying brightness of the display are applied upon each of the source electrodes by the source electrode driving circuit to apply the electrodes upon the liquid crystal through the switching transistors. Therefore the display operation is effected.
The conventional source electrode driving circuit is composed of a large scale integrated circuit (LSI), as shown in FIG. 8, when the driving electrodes are many in number. In this case, as the above-described sampling hold operation is required to be continuously effected about all the LSIs, the output of the last stage of the shift register circuit 61 of each LSI is adapted to be inputted into the input terminal of the shift register circuit 61 of the next LSI. The shift register circuit 61 of each of the LSIs are adapted to effect, in all, the same operation as that of one shift register circuit, thus the continuous display is provided by the plurality of LSIs.
Generally, in the driving circuit for a matrix type liquid crystal display apparatus, digital signals are used with analog signals, with an influence problem that noises are mixed from the digital signals to the analog signals. Particularly, in the use as the display apparatus for a television image display appliance of a small type, high-frequency noises radiated into the air are mixed into the antenna of the appliance itself. This occurs in addition to the direct influences through the power wire, signal wire, so as to disturb the display images. Furthermore, as comparatively large current flows at a moment the level of the digital signal varies, linear image disturbances which are synchronized with the digital signals appear on the picture image because of the influences thereof.
As a countermeasure against the above-described problem, each digital signal whose level varies while the sampling operation is effected, is attempted to not be used as much as possible within the source electrode driving circuit. Adding a circuit for removing the high frequency component of the signal has been considered in a position as near as possible to the supply end of each digital signal.
However, when a plurality of LSIs are connected in concatenated construction in the conventional source electrode driving circuit, the connection signals between the LSIs become necessarily digital signals. The digital signal's level varies within the sampling operation period. This therefore causes such image disturbances as described hereinabove. As the LSIs are often provided normally in high density, it is often that effective noise countermeasures cannot be taken against the connection signals near the LSIs.